There is a known limitation about join() functions that are not supported when running in live queries — the details are explained at summary_query-joins-performance.

This limitation causes these queries not truly running live in your widget, but running repeatedly instead, to show results that are as recent as possible.

When you create a widget with such a query, an indicator in the User Interface notifies you on how old the query is — that is, when it was the last time it has been executed (Just now, 1 minute ago, etc.):

Figure 128. Repeated Query Indicator